As a prelude to describing products and processes according to the present invention, some background on the fields of dual-chambered syringes and injection molding techniques for medical barrels and other such thin-walled tubular structures, is appropriate.
Dual-chambered syringes, such as those described in U.S. Pat. Nos. 5,605,542 and 6,817,987, which are incorporated herein by reference in their entireties, typically include a tubular barrel with an axially movable partition disposed within the barrel. The partition separates and seals off front and rear syringe chambers, one from the other. The purpose of these separate chambers is to enable the syringe to hold two separate substances, which are generally combined by actuating the syringe at the time of use. For example, the front chamber may contain a lyophilized drug product and the rear chamber may contain a liquid solvent to be mixed with the drug product at the time of use. By maintaining these substances in separate chambers until the time of use, the stability of the preparation may be improved.
When the syringe is actuated at the time of use, the partition moves axially, towards the front of the syringe (i.e., towards the needle). In order to enable fluid communication between front and rear chambers at the time of use, a dual-chambered syringe typically has a bypass groove along a portion of the syringe's inner wall. The bypass groove tends to have a length that exceeds the length of the partition. As such, when the partition is driven forward and seated over the bypass groove, fluid from one chamber is permitted to flow around the partition via the bypass groove into the other chamber, thereby combining the two substances that were initially segregated.
As shown in FIG. 1, which is a reproduction of FIG. 1 from U.S. Pat. No. 5,605,542, the bypass groove of the syringe (reference numeral 6 in that figure) is a recess in the syringe barrel that is formed by a bulging of the outer wall of the barrel. Likewise, as shown in FIG. 2, which is a reproduction of FIG. 1 from U.S. Pat. No. 6,817,987, the outer wall of the syringe barrel adjacent to the bypass groove (reference numeral 9 in that figure) bulges outwardly. This appears to be typical configuration for bypass grooves in the dual-chambered syringe art. While this configuration may be suitable for syringes made from glass, there are challenges associated with producing plastic dual-chambered syringes having functional bypasses with good flow properties. These challenges arise from the nature of typical injection molding processes used for making plastic syringe bodies. To better convey the nature of such challenges, a background on the injection molding process, as it pertains to medical barrels (e.g., syringes), is now provided.
FIG. 3 illustrates an exemplary embodiment of a molding assembly for molding a thin-walled plastic tubular structure, e.g., a syringe barrel. An exemplary syringe barrel 12 that may be molded using the molding assembly is shown in FIGS. 4 and 5.
The molding assembly includes one or more mold cavities 142. The mold cavity 142, shown in detail in FIG. 3, is configured for molding a syringe barrel 12 of the type shown in FIGS. 4 and 5, although it should be understood that the mold cavity 142 may be modified to produce similar tubular thin-walled structures other than syringe barrels, e.g., cartridges, parenteral containers, and the like.
The mold cavity 142 is formed as a cylindrical opening 144 in a molding block of the assembly. The opening 144 extends in direction D to an inner surface 146 of the molding block. A sleeve 148 may be fitted within the molding block and define the opening 144. The sleeve 148 is formed of a material capable of appropriately distributing heat during molding and may include a plurality of cooling channels 150.
An inner core 152 fits within the opening 144 to define the interior 20 of the syringe barrel 12. The inner core 152 is of a cylindrical shape similar to that of the opening 144, but is of a smaller diameter. A molding space 154 is defined between the opening 144 and the inner core 152. The molding space 154 is sized and shaped to form a syringe barrel 12, such as that shown in FIGS. 4 and 5. The inner core 152 projects from a core plate, which is located outward in the molding assembly with respect to the molding block. An injector 156 extends through a portion of the molding block for injecting thermoplastic molding material (e.g., a cyclic olefin) into the mold cavity 142 during molding.
Upon initiation of a molding operation, a core plate is first moved in direction D, such that the inner core 152 is moved into the opening 144, to create a syringe barrel 12 shaped molding space 154. Molten molding material is then injected into the mold cavity 142 through the injector 156. The molding assembly may be heated before or during this portion of the procedure to permit sufficient flow of the molding material to fill the entire molding space 154. The molding material flows through the molding space 154.
The molding material is then permitted to cool below its melting point, and in some embodiments may be actively cooled by cooling of the assembly, for example by injecting a coolant into cooling channels 150 where provided. The core plate is moved outward in direction D, withdrawing the core 152 from the interior 20 of the molded syringe barrel 12. The syringe barrel 12 is withdrawn from the mold cavity 142 by being moved outward in direction D, i.e., in a direction along the axis of the syringe barrel 12.
Injection molding is the most common and preferred method of fabricating plastic parts because of its speed of production, low labor costs and design flexibility. As mentioned above, however, there are challenges to incorporating a standard, outwardly protruding bypass, in a plastic injection molded syringe barrel. One such challenge is that an outward protrusion or bulge from the outer wall of the syringe barrel would prevent the syringe from being withdrawn from the mold cavity in a direction along the axis of the syringe barrel. While a mold cavity may be configured to create a protrusion from the outer wall of the syringe, such a mold would need to be formed from two mold blocks joined together. Once a syringe barrel is formed and cooled, the mold blocks would separate enabling withdrawal of the syringe barrel. This process, however, would imprint a line on the syringe barrel along the seam in which the mold blocks had been joined. Syringe bodies often need to be transparent and unblemished to enable visual inspection of the nature of the syringe's contents (e.g., to confirm that no particulates are suspended therein, etc.). A line along the syringe barrel or other visual blemishes could frustrate this purpose. While withdrawal of the syringe barrel from a solid one-piece mold cavity in an axial direction avoids the problem of the line blemish, an outward protrusion on an injection molded syringe barrel prevents withdrawal of the syringe barrel in an axial direction for reasons discussed above.
What is needed, therefore, is a plastic injection molded syringe barrel with a bypass in the inner wall that does not cause the outer wall to bulge outwardly. More broadly, what is needed are methods and apparatuses for injection molding a walled structure, in which one or more recesses (including a bypass groove having good flow properties) are impressed into an inner wall of the structure without altering the surface geometry of the outer wall of the structure.
The foregoing Background of the Invention should be regarded as part of the specification of the invention. It is intended that components, elements and aspects of dual chambered syringes, injection molding apparatuses and processes for injection molding described in the Background of the Invention may be used as support for aspects of the claimed invention.